Microthrusters are becoming increasingly vital onboard modern spacecraft. While many spacecraft systems can be minimized with the application of new technology, hardware limitations and power requirements still constrain traditional propulsion system size. The proportion of the propulsion system increases as the size of a spacecraft is reduced. This limiting factor in spacecraft design results in the fact that many of today's micro- and nanosatellites have no onboard propulsion systems, even though these smaller spacecraft have similar mission requirements of their larger brethren.
There are six features often included in the design of spacecraft: modularity, maneuverability, maintainability, lifetime, autonomous operation, and launch/hardware cost. All of these aspects become more constrictive on the smaller spacecraft design. Both chemical and electric propulsion systems not only address these issues, but should still deliver a comparable propulsive performance to that of larger systems. In particular, electric propulsion systems should take into account power limitations as well. The integration of electric microthrusters relies on reducing both the power and voltage requirements while ensuring reliable, long-term performance.
Since the 1990s, electric propulsion (EP) has become a vital part of spacecraft propulsion for a wide spectrum of space missions and applications. These systems can provide significant performance benefits compared to conventional chemical systems. Commercial satellite manufacturers have embraced EP due to the significant economic advantages as well. To date, electrothermal, electrostatic and electromagnetic systems propel close to 200 spacecraft in various mission scenarios spanning from low earth orbit (LEO) to interplanetary trajectories. However, these systems employ electric thrusters which function best at power levels greater than 1 kW.
Electric propulsion in general provides a more propellant efficient, higher specific impulse method for in-space propulsion when compared with traditional chemical systems. While this attribute makes electric propulsion attractive for longer duration missions, this increase in specific thrust (Isp) adversely lowers the available thrust. This lower thrust level often limits the electric propulsion operation to that of space missions, where higher thrust levels are not required. This thrust limitation also makes electric propulsion attractive for station-keeping maneuvers, low-thrust attitude control, and low thrust inter-planetary missions.
Regardless of the method of adding energy to a fluid to provide thrust, there is always a need to achieve as much thrust as possible from the fluid. By increasing net thrust at a particular mass flowrate, the size and weight of the microthruster can be better optimized for the particular application. Various embodiments of the present invention provide novel and nonobvious ways in which to increase thrust.